The aims of the Tissue Banking and Molecular Assessment Core are to: 1. Receive, process, store, and retrieve samples from children and adults with acute lymphoblastic leukemia and appropriately distribute material to the scientific and clinical projects within the Program. 2. Perform real time quantitative polymerase chain reaction assays using as markers the unique IgH and TCR rearrangements identified in the diagnostic patient samples. Core C will work to obtain peripheral blood and bone marrow samples, isolate the mononuclear cell fraction and cryopreserve cells, RNA and DNA from tumor samples. The Core will distribute these samples to the Projects as required and will prioritize the use of samples in which cell numbers are limiting. This will allow for distribution of the most appropriate samples to each Project to achieve the scientific aims of Projects 1, Project 3, Project 4, Project 5, and Project 6. The Core will provide molecular biologic analysis of immunoglobulin heavy chain (IgH) and T cell receptor (TCR) gene rearrangements in diagnostic samples and perform quantitative polymerase chain reaction assays in post treatment samples using as markers these patient specific gene rearrangements. The goal is to assess the dynamics of the eradication of minimal residual disease and identify patients at sufficiently high risk of relapse to be candidates for experimental treatment approaches in Project 6, using the targets identified within Projects 1, 3, 4 and 5. The Core is essential to achieve the full translational potential of this Program.